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NICER–NuSTAR Observations of the Neutron Star Low-mass X-Ray Binary 4U 1735–44

Ludlam, R. M. and Cackett, E. M. and García, J. A. and Miller, J. M. and Bult, P. M. and Strohmayer, T. E. and Guillot, S. and Jaisawal, G. K. and Malacaria, C. and Fabian, A. C. and Markwardt, C. B. (2020) NICER–NuSTAR Observations of the Neutron Star Low-mass X-Ray Binary 4U 1735–44. Astrophysical Journal, 895 (1). Art. No. 45. ISSN 1538-4357. doi:10.3847/1538-4357/ab89a6.

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We report on the first simultaneous Neutron Star Interior Composition Explore (NICER) and Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the neutron star (NS) low-mass X-ray binary 4U 1735−44, obtained in 2018 August. The source was at a luminosity of ~1.8 (D/5.6 kpc) ² × 10³⁷ erg s⁻¹ in the 0.4–30 keV band. We account for the continuum emission with two different continuum descriptions that have been used to model the source previously. Despite the choice in continuum model, the combined passband reveals a broad Fe K line indicative of reflection in the spectrum. In order to account for the reflection spectrum we utilize a modified version of the reflection model RELXILL that is tailored for thermal emission from accreting NSs. Alternatively, we also use the reflection convolution model of RFXCONV to model the reflected emission that would arise from a Comptonized thermal component for comparison. We determine that the innermost region of the accretion disk extends close to the innermost stable circular orbit (R_(ISCO)) at the 90% confidence level regardless of reflection model. Moreover, the current flux calibration of NICER is within 5% of the NuSTAR/FPMA(B).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ludlam, R. M.0000-0002-8961-939X
Cackett, E. M.0000-0002-8294-9281
García, J. A.0000-0003-3828-2448
Strohmayer, T. E.0000-0001-7681-5845
Guillot, S.0000-0002-6449-106X
Jaisawal, G. K.0000-0002-6789-2723
Malacaria, C.0000-0002-0380-0041
Fabian, A. C.0000-0002-9378-4072
Markwardt, C. B.0000-0001-9803-3879
Additional Information:© 2020 The American Astronomical Society. Received 2020 February 21; revised 2020 April 4; accepted 2020 April 14; published 2020 May 22. Support for this work was provided by NASA through the NASA Hubble Fellowship grant #HST-HF2-51440.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. J.A.G. acknowledges support from NASA grant 80NSSC19K1020 and from the Alexander von Humboldt Foundation. E.M.C. gratefully acknowledges support through NSF CAREER award number AST-1351222. C.M. is supported by an appointment to the NASA Postdoctoral Program at the MSFC, administered by USRA. Facilities: ADS - , HEASARC - , NICER - , NuSTAR. - Software: heasoft (v6.26.1), nustardas (v1.8.0), nicerdas (2019-06-19_V006a), xspec (v12.10.1).
Group:Space Radiation Laboratory, NuSTAR
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51440.001
Alexander von Humboldt FoundationUNSPECIFIED
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:Accretion ; Neutron stars ; Low-mass x-ray binary stars
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Accretion (14); Neutron stars (1108); Low-mass x-ray binary stars (939)
Record Number:CaltechAUTHORS:20200522-131436417
Persistent URL:
Official Citation:R. M. Ludlam et al 2020 ApJ 895 45
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103422
Deposited By: Tony Diaz
Deposited On:22 May 2020 20:52
Last Modified:16 Nov 2021 18:21

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